Casters are commonly attached to transport vehicles, such as carts, trailers, trucks, or dollies, and allow for rolling movement of the transport vehicle along a ground surface. Casters generally include a horn, also referred to as a yoke, having a pair of legs that extend downwardly and support a caster wheel that rolls along the ground surface.
Casters may be permitted to rotate about a vertical axis (termed “swivel”), or they may be fixed or restricted (termed “rigid”). Swivel casters generally include a horn base that is rotatably coupled with a mounting plate or a stem such that the horn and caster wheel may swivel about the vertical axis relative to the caster mounting plate or stem. This swiveling action allows for multi-directional rolling movement of the caster wheel, which enables steering and turning of the vehicle and thereby enhances vehicle maneuverability. In contrast, rigid casters include a horn that is rigidly attached to the mounting plate, such that the horn and caster wheel are fixed relative to the mounting plate and do not rotate about a vertical axis. Transport vehicles may be fitted with one or more swivel casters and one or more rigid casters depending on the application and transport design. In a common arrangement, a vehicle may include swivel casters on an rear, operator-end of the vehicle, and rigid casters on the front, opposing end of the vehicle. For improved vehicle maneuverability in tight spaces, the vehicle may be provided with swivel casters at both vehicle ends. An example of this is a common furniture dolly or a grocery cart.
A problem common to vehicles equipped with multiple swivel casters is the propensity of the swivel casters to “lock up” and thereby create significant resistance to rolling movement of the vehicle. Such “locking up” may occur when the vehicle is temporarily brought to rest and at least two casters are allowed to swivel to positions in which two or more caster wheels become substantially misaligned, such that the caster wheel of one caster is oriented in one direction of travel and the caster wheel of an opposing caster is oriented in a different direction of travel. Such “locking up” of the swivel casters may also occur upon attempts by the operator at sudden and substantial changes in direction of travel of the vehicle. For example, when a vehicle having four swivel casters is pushed toward a wall such that the cart abuts the wall, it may then become difficult to slide the cart along the wall to reposition it. In any such case, a substantial force by an operator may be required to “break” the locked condition of the swivel casters, thereby creating risk of injury to the operator. These problems are often magnified when the swivel casters are heavily loaded in a vertical direction, as is often the case with heavy-duty swivel casters used in industrial applications.
The “locking up” effect described above is due primarily to the concentric bearing design of conventional swivel casters, which defines a single vertical swivel axis. Prior attempts to remedy the above-described drawbacks have yielded swivel casters having two swivel axes defined by two separate, non-overlapping bearing assemblies spaced apart from each other, thereby presenting a bulky structural design. Accordingly, there is a need for an improved swivel caster that addresses the “locking up” difficulty of conventional swivel casters when mounted on a vehicle, while also presenting a compact structural design that is suitable for heavy-duty, industrial applications.